Automobile air conditioner test and service equipment

ABSTRACT

Electronically automated equipment utilized for diagnostic evaluation and repair of automobile air conditioning systems. Test connections provide sensors to measure the various pressures and temperatures in the operating system which are selectively connected to appropriate readout devices. Various hand actuated switches are provided to sequentially actuate the respective test circuits. If the circuits indicate a fault within the air conditioning system, the balance of the manually operated switches are operable to evacuate the system to enable repair and subsequently to recharge the system to an optimum operating condition. Additional features, in keeping with the electronic nature of the system, are capacitive measurement device to precisely determine the amount of refrigerant to be charged into the system, and a thermostatically controlled heater to assure suitable refrigerant temperature and pressure during the charging cycle.

United States Patent Motl AUTOMOBILE AIR CONDITIONER TEST AND SERVICEEQUIPMENT Daniel M. Motl, New Brighton, Minn.

Assignee: Allied Power Industries, Inc., Milwaukee, Wis.

Filed: April 8, 1971 App1.No.: 132,309

Inventor:

US. Cl. ..73/432 R, 62/ 125, 116/ 129 T Int. Cl. ..G01m 19/00 Field ofSearch ..73/168, 432 R; 62/125, 127,

References Cited UNITED STATES PATENTS 10/1939 Kucher ..73/432 R 2/1956Sahs ..73/432 R 3/1963 Kayan ..62/127 4/ 1963 Ehrens ..73/168 ATMOSPHERETOP CHARGING CYLINDER Primary Examiner-S. Clement SwisherAttorney-Frederick E. Lange, William C. Babcock and Jon F. Tuttle [57]ABSTRACT Electronically automated equipment utilized for'diagnosticevaluation and repair of automobile .air conditioning systems. Testconnections provide sensors to measure the various pressures andtemperatures in the operating system which are selectively connected toappropriate readout devices. Various hand actuated switches are providedto sequentially actuate the respective test circuits. If the circuitsindicate a fault within the air conditioning system, the balance of themanually operated switches are operable to evacuate the system to enablerepair and subsequently to recharge the system to an optimum operatingcondition. Additional features, in keeping with the electronic nature ofthe system, are capacitive measurement device to precisely determine theamount of refrigerant to be charged into the system, and athermostatically controlled heater to assure suitable refrigeranttemperature and pressure during the charging cycle.

11 Claims, 7 Drawing figures ()TO SYSTEM HIGH SIDE (3T0 SYSTEM LOW SIDE(DBLEED TO ATMOSPHERE Patented Aug. 29, 1972 3 Sheets-Sheet 1 TO SYSTEMHIGH SIDE TO SYSTEM LOW SIDE BLEED TO ATMOSPHERE ummImmosrrd [\VENTORDaniel M Mail Patented Aug. 29, 1972 3 Sheets-Sheet 5 8 5 W 7 1 Z 7 m 75 5 z w% a a w a m 4 WW 2 2 Z k m .w. 4 l I a. m m p I w CHARGINGCYLINDER '7 Jfia 4r ram/EV AUTOMOBILE AIR CONDITIONER TEST AND SERVICEEQUIPMENT BACKGROUND OF THE INVENTION The invention is designed toperform diagnostic testing and servicing of automobile air conditionersin a faster, simpler, and more reliable way than prior devices, therebysaving time and enabling the work to be done by a less skilled operator.Prior and existing devices have required the operator to refer to anoperations manual to determine how to hook up, valve by valve, each lineand gauge prior to testing an air conditioning system. In addition,prior systems employ such devices as sight gauges to determine theamounts of refrigerant that is to be charged into an automobile airconditioning system. As is common with sight gauges, and particularly inan environment such as the one this invention is intended to beused,difficulties in reading the level are present due to the location ofglass, which, of necessity, must be at the same level as the cylinder.Problems also arise because asight glass is an absolute volumetricdeterminate which does not compensate for volumetric changes due totemperature changes. In the prior systems after diagnostic proceduresand evaluation was complete, reference was again required to anoperating manual to determine the proper arrangement and manipulation ofthe valves normally existing in a conventional system as well as theoperational technique to accomplish servicing.

SUMMARY The present invention due to automated electronic deviceseliminates manual set up error throughout the performance of diagnosisand service. This is accomplished by providing electronic solenoidvalves actuated by push button switches. Diagnosis is performed bysequentially actuating the switches, some of which control as many asthree solenoid valves. The test results are electronically connected toa meter board which carries meters relevant to each of the tests andsubsequent servicing. Utilized are specially created meter faces whichindicate defects in the existing air conditioning unit and whichareemployed to correct those defects when servicing the air conditioningsystem. If recharging is necessary due to a low supply of refrigerant orrepair of the system, precision measurement of the amount of refrigerantto be recharged is accomplished through the use of an electroniccapacitive sensor integrally formed with the charging cylinder. Thiselement of the invention not only provides a more accurate readout butessentially eliminates problems due to the location of the cylinder andtemperature changes which normally interfere with accurate readingsobtained from a sight gauge. Since the reading is electronic, it can belocated at a point remote from the cylinder itself. Also, the reading isbased on the mass or weight of refrigerant so that volumetric expansionof the liquid being measured, due to a temperature increase, does notchange the reading. The charging cylinder is also provided with athermostatically controlled heater which maintains the refrigeranttemperature and pressure above that in the air conditioner, to insure anadequate flow rate when charging.

BRIEF DESCRIPTION OF THE DRAWINGS ing the electrical circuitry of myinvention;

FIG. 4 is a perspective view, partly in section, showing the refrigerantcharging cylinder and associated capacitive element which enablesaprecision readout of the amount of refrigerant charged into the airconditioning system;

FIG. 5 is an end view partly in section taken along I the line 5-5 byFIG. 4 which shows the ring heater utilized in the charging cylinder;

FIG. 6 is a schematic of the operating details of the ring heater; and

FIG. 7 shows one of the various dials which references ambienttemperature which may be employed in my invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT An understanding of the generalappearance of the preferredembodiment may be readily obtained withreference to FIG. 1. To enable the operable connections and readoutdevices to be at a convenient eye level a base 1 1 is provided which issuitable for containing items useful in the operation of the apparatus.Provision may be made in the base portion of the apparatus for storagefacilities, such as sliding drawers, to store the various toolsnecessary for hookup and repair of an automobile air conditioningsystem. Swivelly attached to each corner of the base are conventionalcaster wheels 13, 14, 15 to enable the apparatus to be readily portable.F ixedly secured to the top of the base 1 I is a work table 17.

Supported above the work .table by any suitable means such as the sidemembers 19 and 20 shown in FIG. I is a housing 24 which contains arefrigerant storage drum, an evacuator pump, a charging cylinder withassociated flow paths and the internal circuitry, all shown anddiscussed in greater detail below. As shown, handles 31 and 32 may beprovided attached to the side members 19 and 20 to enable an operator toeasily manipulate the portable diagnostic and service apparatus. On theface 34 of the equipment housing 24, push buttons 36-42 are providedwhich operate solenoid valves located internally in the housing (shownin FIG. 2) as well as an operating knob for a rotary switch 44 whichconnects the electronic sensing elements, such as therrnistors, to theappropriate scale of the readout device 55. It should be understood thatinstead of the rotary switch 44 all switches could be push button forease of operation. Also on the outer face of the housing are connectors47, 48, 49, and 50 suitable for connection to pressure hosing 61, 62 and64 to attach to the automobile air conditioning system. These pressureconnections can be designated bleed, auxiliary low pressure, system lowpressure," and system high pressure, respectively.

Also carried on the face of the housing are the meters 51-55 whichindicate the operating parameters of the air conditioning system priorto and during testing. Meters 51 through 54 have dials designed toindicate auxiliary low pressure, system low pressure, system highpressure, and charging cylinder pressure, respectively. The low pressuremeters 51, 52 are also inscribed with indicia at the low end to enablevacuum pressures to be read. Meter 55 selectively indicates pounds ofrefrigerant charged into the system, temperature, engine speed, and DC.voltage. A unique feature of meter 53 is shown in greater detail in FIG.7 and is discussed in greater detail below.

The unit is connected by means of flexible hoses 61 and 62 which extendfrom the system low pressure connection 49 and system high pressureconnection 50 and are attached to the air conditioner low side and highside service fittings, respectively, (usually located on or near the airconditioning compressor). In the case of Chrysler Corporation vehicleshaving an evaporator pressure regulator (EPR) valve, a compressorsuction fitting is provided and an additional hose 64 connection is madebetween the auxiliary low pressure fitting 48 of the tester and thiscompressor suction fitting. A thermistor temperature measuring system isincluded, with provisions for connecting three separate probes havingflexible leads in sufficient length to permit monitoring temperatures atdesired locations on or near the air conditioner. Exemplary locations ofthese thermistors would be the ambient air temperature near thecondenser, the cold line temperature, and evaporator outlet airtemperature which can be measured at a cold air vent in the passengercompartment. A voltage measuring feature is also incorporated, with clipleads, which can be connected to various electrical components such asthe compressor clutch, fan motors and control switches and provision ismade for reading all pressure, temperature and voltage values on thepanel mounted meters 51-55 discussed above. The voltage measuringdevices and pressure gauges may be conventional, and, as noted above,pressure reading capability should include the ability to read vacuumpressures as low as 30 inches of mercury. In the system described vacuumpressures are read at the low end of the pressure meters, 51 and 52.

. The basic diagnostic procedure consists of operating the airconditioner until a stabilized condition is reached, then observingthesystem pressures which are transmitted through the hoses 61 and 62(and hose 64, if used) and indicated by the gauges 52 and 53 on thefront panel 34. These pressure readings are correlated with otherobservations, such as temperature, to provide an indication of variousdisorders such as loss of refrigerant, contamination of refrigerant,compressor malfunction or expansion valve malfunction.

When the testing procedure has been completed, the air conditioner isshut off. Then, depending on the test results, one or more of thefollowing procedures may be required to service the air conditioner:addition of a partial refrigerant charge to facilitate lead testing orto correct a small refrigerant loss; bleeding all the refrigerant out ofthe system to permit repair or replacement of components; drawing avacuum on the system to remove air, moisture and other contaminants; andadding a complete charge of fresh refrigerant, in a measured quantitycomplying with the manufacturers specification.

Initially all valves are closed, the hosing 61 and 62 going to thefittings 49 and 50 for the system low pressure and system high pressureare attached to the automobile air conditioning unit. The diagnosis andservice apparatus is then energized by depressing first the power on-ofibutton 65, shown in FIG. 1, and then sequentially the test button 36,also shown in FIGS. 1 and 3. As shown in FIG. 2, to assure that testconditions are not affected by the valving, the Off/test push button 36disconnects the solenoid coils which operate the valves, while the testcircuits remain energized.

The car is then started and run at a speed between 1,400-1 ,700 rpm,read on meter 55, with the air conditioner on full cold forapproximately 10 to 15 minutes or until the pressure stabilizes. Thegauge 52 readings for system low pressure should be between 15 to 30 psifor most automobile air conditioning systems which utilize no auxiliaryvalves. For Chrysler products which utilize an evaporator pressureregulator (EPR) valve the gauge 52 reading should be between 22 and 30psi and for General Motors products which utilize a pilot operatedabsolute (POA) valve to prevent evaporator iceing, gauge 52 readingshould be between 28 and 33 psi. The system high pressure should fallbetween pressures which correspond to ambient temperature within therange set forth on scale 69 and scale 70 in FIG. 7.

The scales 69 and 70 have been derived from the relationship whichexists in the properly operating system between the high siderefrigerant pressure, the condenser temperature and ambient temperature.A conventional pressure scale 72 is inscribed with appropriate indiciaas occurs in a conventional system. The non-linear ambient temperaturerange limitations are set forth in units of temperature in a concentricscale circumferentially inscribed in radial alignment with the pressurescale. Temperature scales 69 and 70 are disposed upon opposite sides ofa common base line, being displaced from each other circumferentially.Due to this arrangement, the operator need only determine whether theindicating pointer falls within the range limited by the actual ambienttemperature as indicated on the two displaced scales 69 and 70. Forexample, for an ambient temperature of the pressure reading opposite 90on scale 69 is psi and that opposite 90 on scale 70 is psi. Thus for theambient temperature of 90 the system high pressure should range betweenl75 psi to 195 psi. If either of these readings is above or below theexpected reading, or if the thermistors indicate a problem in the airconditioner such as a high temperature in the car, then reference may bemade to a technical manual which indicates approximately 15 diagnosticprocedures to determine the nature of the defect in the air conditionersystem.

Where, as is the case with Chrysler Corporation vehicles, a hose 64 isconnected between the auxiliary low pressure fitting 48 of the testerand the compressor suction fitting of the air conditioner, the auxiliarylow pressure read on meter 51 (corresponding to the compressor suctionpressure) is compared with the system low pressure read on meter 52(corresponding to the evaporator pressure). If the differential betweenthese two pressures is too great or too small, then the evaporatorpressure regulator is not working properly and it is necessary either toreplace it or repair it.

The system mechanical and electrical circuitry utilized to perform thevarious testing and servicing functions are shown schematically in FIGS.2 and 3. They show in block diagram form the interrelationship of thepush buttons 36 to 42 and the solenoid valves 81 through 90 controlledthereby and the principles of their operation. Each solenoid valve 81through 90 is operated by an associated solenoid coil 101 through 110,respectively. These solenoid coils are shown in FIG. 3. The solenoidvalves are all of the normally closed type which are opened uponenergization of their associated solenoid coil.

Referring to FIG. 2, the flow paths required for the various modes ofoperation are controlled by the electric solenoid valves 81 to 90 whichare energized to open in various combinations by the series ofinterlocked push-button switches 36 to 42 (as shown in FIG. 3). Five ofthese valves 81 to 85 are interconnected through a main control manifold92 and the other five 86 to 90 are used to direct the flow to and fromthe charging cylinder 94. For purposes of clarity, the following chartlists these valves in numerical order with a cylinder (two valves backto back) Seven push buttons 35-42 are used to operate the solenoidvalves 81-90 in the required combinations. Six of these 36-41 areinterlocked so that whenever one of them is depressed it will remain inthat position until unlatched and will, at the same time, unlatch any ofthe other five buttons which was previously depressed. The seventhbutton 42 (designated Cylinder bleed) works independently of the others36-41 and remains depressed only when manually held in that position.The designation of the push buttons and their respective function isshown in the following table:

Push Button Valves Description Designation Energized Off/test 36 noneAll valves closed.

Test circuits remain energized.

System bleed 37 81, 82, 83 Both sides of system bled to atmospherethrough manifold 92.

Restrictor incorporated in bleed line to limit flow velocity and preventloss of oil. Both sides of system Evacuate 38 81, 82, 84

Vapor charge 39 82, 85, 86

Liquid charge 40 81 85, 88

Cylinder fill 41 89, 90

Cylinder bleed 42 87 As noted above, the air conditioner must be inoperation during the functional testing procedure. It is also frequentlydesirable that it be in operation during the vapor charge" condition sothat the pumping action of the compressor will serve to assist the' flowof refrigerant into the system. On the other hand it is important toavoid actuation of the system bleed, evacuateand liquid charge functionsunless the air conditioner has been shut off, as serious damage mayotherwise occur. To guard against this possibility a pressure switch canbe incorporated that senses the on or off condition of the airconditioner by responding to the changes in pressure which occur betweenthese .two conditions. Electrically the switch would be connected toprevent valves 81, 83, 84 and 88, and the vacuum pump 96, from beingenergized when the air condiof the push buttons 37-42 mentioned earlierand shown in FIG. 1. These push buttons 37-42 have designations listedin the first column of Table 2. One side of all of the solenoid coils isenergized from one side of the AC. power source from point 118 throughconductor 119 and switch 36 to bus bar 122. The other side of the'solenoid coils is energized from point 111 on the power source throughconductor 113 to the bus bar 1 16.

When the first push button 37, designated system bleed, is depressed,switches 130, 141 and associated therewith are closed and the solenoidcoils 101, 102 and 103 of solenoid valves 81, 82 and 83 are energized asfollows. Coil 101 is energized by a circuit extending from bus bar 122through conductor 134, switch 130, conductors 128 and 126, solenoid coil101, to the other bus bar 1 16. Solenoid coil 102 is energized by acircuit extending from bus bar 122 through conductor 134, switch 141,conductors 138 and 136, and solenoid coil 102 to the bus bar 116.Solenoid coil 103 is energized by a circuit extending from the bus bar 116' through conductor 134, switch 145, conductor 143, and solenoid coil103 to the bus bar 116. As can be seen from FIG. 3 all of thecombinations can be similarly traces. For example, the button 40designated liquid charge actuates, from Table 2, valves 81, 85 and 88which are energized as follows. Solenoid coil 101 is energized by acircuit extending from bus bar 122 through conductor 150, switch 148,conductors 146 and 126 and solenoid coil 101 to the bus bar 116.

Solenoid coil 105 is energized from a circuit extending from bus bar 122through conductor 150, switch 155, conductors 153 and 152, and solenoidcoil 105 to the bus bar 116, and solenoid coil 108 from bus bar 122through conductor 150, switch 157, conductor 156 and solenoid coil 108to the bus bar 1 16.

Additionally, in the evacuate cycle when both sides of the system areconnected to the vacuum pump 96,

the vacuum pump 96 is energized through a relay 158 which is energizedby push button 38, energization being through a circuit extending fromthe bus bar 122 through conductor 166, switch 164, conductors 162 and160, and relay coil 158 to the other bus bar 116. When this isenergized, relay coil 1158 pulls in relay switch 168 which energizes thevacuum pump 96 from one side of the primary source through conductor170, relay switch 168, vacuum pump 96, and conductor 172 to the otherside of the primary source. Thus, in addition to solenoid valves 81, 82and 84 being opened, the vacuum pump 96 is energized.

The balance of FIG. 3 shows the circuitry, in block diagram andschematic form, which is utilized to obtain and monitor the applicableparameter values. A D.C. regulated power supply 180 supplies appropriatevoltages. Temperature values are obtained utilizing a Wheatstone bridgecircuit 182 in which the unbalance caused by temperature sensitivethermistors 185, 186 or 187 is read by the meter 55. A conventionalswitching circuit 187, is used to select the desired thermistor 185, 186or 187 to be measured and the appropriate readout scale on the meter 55.As shown in FIG. 3, the balance of the Wheatstone bridge is comprised ofresistors 190, 191 and 192, in the other legs of the bridge, as well asa calibrating resistor 194 in the meter circuit. The switching circuit,as shown in FIG. 3, is a three pole switch with two contacts beingutilized to connect the meter across the appropriate bridge and thethird contact being utilized to selectively insert the chosen thermistor185, 186 or 187 into the bridge circuit. However, it should beunderstood that any switching circuit, such as a rotary switch 44 or aseries of push-button switches, could be utilized.

Also shown in the center portion of FIG. 3 in block diagram form is thecircuitry utilized to assure that the proper engine speed for testing isattained and its connection to the automobile engine. The numerals 202,204 designate the conventional distributor switch commonly referred toas the points. This switch is periodically opened and closed by adistributor cam 206 with a frequency depending upon the speed of theengine. Connected across the points is the conventional distributorcapacitor207. The voltage across the points is applied to the inputterminal of a square wave generator 208 to produce a series of pulses ofrelatively uniform height and of a frequency corresponding to that ofthe voltage pulses across the distributor points 202, 204. These outputpulses are in turn supplied to an integrator and rectifier 210 toproduce a D.C. voltage, the magnitude of which is dependent upon thefrequency of the pulses across the distributor points 202, 204 and henceupon the engine speed. The output voltage of this integrator andrectifier 210 is applied through lines 212 and 214 and contacts 197 and198 of three pole switch 187 to the movement of the meter 55 to cause adeflection of the needle by an amount dependent upon engine speed.

The amount of refrigerant in the charging cylinder 94 is measuredutilizing a capacitive measurement device which is discussed below. Aconventional Colpitts oscillator 220 is employed to create analternating signal through a capacitance bridge 222 which is used tomeasure the refrigerant mass. The basic elements of the capacitancebridge can be, as shown in FIG. 3, resistances 224 and 225 and acapacitance 227 comparable in magnitude to the expected range, of thecapacitance of the charging cylinder 94. The zeroing of the capacitancebridge 222 may be conventionally accomplished using the substitutionmethod (not shown). As above, the appropriate meter scale is selectedwith the use of the switching device 187 wherein the meter 55 isconnected across the bridge with leads 230 and 231. To utilize the samemeter 55 a conventional diode dicated a part must be repaired. The firststep would be to bleed both sides of the automobile air conditioningsystem to atmosphere. This is accomplished by pressing push button 37designated system bleed which opens valve 81, 82, and 83. As shown inFIG. 2, both sides of the system are bled to atmosphere, the high sidethrough valve 81, through the manifold 92 and through valve 83 toatmosphere and the low side through valve 82, through the manifold 92,and through the valve 83 to atmosphere. The next step would be to repairor replace the defective component. Then the air conditioning systemwould be evacuated to remove air, moisture and other contaminants. Thisis accomplished by depressing the evacuate push button 38 to open valves81, 82 and 84 and energizing the vacuum pump 96 by means of thecircuitry mentioned earlier. Evacuation is accomplished in the samemanner as above with valve 84 being opened, 83 and being closed and bothsides of the system being evacuated through valve 84 by the vacuum pump96.

The addition of fresh refrigerant is accomplished by first depressingthe cylinder fill button 41 which opens valves 89 and causingrefrigerant to flow from the supply drum through flow line 231, valves90 and 89, and flow line 233 into the bottom of the charging cylinder94. In the event the charging cylinder 94 contains excess back pressuredue to pressure of air or the recent use of the heater 240 on a previousvehicle, then the cylinder 94 can be bled to atmosphere by depression ofthe push button 42 designated cylinder bleed. This causes valve 87 toopen and any vapor in the cylinder 94 will be discharged from the top ofthe charging cylinder 94 through flow line 230 and valve 87 toatmosphere thereby reducing the pressure in the charging cylinder 94 toa pressure lower than that in the supply drum so that the required flowof refrigerant will occur.

An indication of the exact amount of refrigerant in the chargingcylinder 94 is useful when filling the charging cylinder, whentransferring refrigerant to the air conditioning system (referred to ascharging) and also at any time to determine whether there is asufficient amount of refrigerant in the cylinder to accomplish ananticipated procedure. To indicate the exact amount of refrigerant inthe charging cylinder 94, it is measured with a capacitive measuringcircuit 222 and charging cylinder capacitance which compensates forambient temperature in the manner described below.

Most commonly the complete charging of an emptied system is accomplishedthrough the use of the liquid charge button 40 which forces refrigerantin liquid form from the bottom of the charging cylinder 94 into the highside of the system. Depression of the liquid charge button 40, causesvalves 81, 85 and 88 to open so that refrigerant flows from the chargingcylinder 94 through flow line 233, valve 88, flow line 235, valve 85,through the manifold 92, and through valve 81 to the high side of thesystem. To assure that all refrigerant is forced into the system thereis a ring heater 240, shown in FIG. and schematically in FIG. .6, on thecharging cylinder 94 which builds the pressure in the charging cylinder94 to a pressure greater than that in the car and forces all refrigerantinto the car in liquid form. As shown schematically in FIG. 6,thermostat 242 has contacts which are normally open when the chargingcylinder is at a suitable temperature.

If the temperature falls below the set point of thermostat 242 thecontacts close and energize relay 243. When this occurs normally openrelay switch 244 closes which energizes the heater 240. The heater 240is powered by the normal full voltage of approximately 120 volts whilethe relay is energized by a substantially lower voltage which can be ofthe order of approximately 24 volts. This is done to maintain safetyrequirements due to the confined space in which the thermostat islocated. Control circuitry may be provided to energize the heater 240automatically whenever refrigerant is being transferred from thecharging cylinder, and deenergize it at all other times. In some casesthere is an excessive build-up of back pressure as charging continues sothat the charging is slowed during charging of the last portion of therefrigerant. In such a case a vapor charge mode is provided. Vaporcharge can also be used for partial charging. In both cases this isaccomplished by depressing the vapor charge button 39 which causesvalves 82, 85 and 86 to open so that refrigerant in vapor form is drawnfrom the top of the charging cylinder 94 and enters the low side of thesystem from flow line 230, through valve 86, through flow line 235,through valve 85, through the manifold 92, and through valve 82 to thelow side. If this is to be done, the car is started and the suction ofthe air conditioning compressor pulls the vapor into the system.

To insure the proper amount of refrigerant to exactly meet themanufacturers specifications a capacitive measuring system has beendevised which is shown in FIG. 4. It is comprised of two concentrictubular conducting surfaces 257 and 258 separated by air and the liquidand vaporized refrigerant as the dielectric. As shown in FIGS. 2 and 4,the charging cylinder 94 is filled from the supply drum through line231, valves 90 and 89, line 233 to the charging cylinder. It enters thebottom of the charging cylinder through a suitable passage way 260 whichterminates in the bottom of the cylinder. Since the inner tubularconducting surface 258 terminates short of the bottom of the cylinder,the

refrigerant and vapor can easily pass into the separation betweensurfaces 257 and 258. The outer tubular surface 257 forms the casing ofthe charging cylinder 94. The inner conducting surface 258 is a thinsheet of conductive material suitably spaced from the outer sheaths bynonconducting spacers 261, 262 and 263 formed out of a suitable acetalplastic such as Delrin.

Electrical contacts 264, 265 are provided to electrically connect thecapacitive surfaces 257, 258 to the bridge circuit 195. As shown in FIG.4, integrally formed with the inner conductive surface 258 is anelectrical post 259. Post 259 is electrically connected to outlet post265 by a lead wire 266 connected to electrical contact 267 which isjoined with post connection 265 by a metal bolt and insulated from thetop 274 with a suitably fitted insulating shield 271 also made of acetalplastic. 0 rings 268, 269, 270 are utilized to seal the top 274 andbottom 273 and the outer casing 257 and the inner orifice in the top 274to the tie rod 276.

The tie rod 276 is constructed from the same type aluminum alloy as theouter shell 257. This causes the shell 257 and the tie rod 276 to expandby the same amount when heated and assures that no leakage of jointswill occur due to temperature changes.

Since the dielectric constant decreases in the same ratio as the densityof the refrigerant, this form of measurement accurately indicates thecorrect weight or mass of refrigerant in the cylinder 94 regardless ofvolumetric changes due to varying temperatures. The approximatenumerical value of capacitance of the device varies between 400 pf whenthe unit is empty to 800 pf when the unit is full.

In general, while I have described a specific embodiment of myinvention, it is to be understood that this is for purposes ofillustration only and that various modifications can be made within thescope of my invention. For example, rather than supporting the housing24 with a base 11, it may be suspended from an overhead rack. Also allcontrols could be manually operable push-button switches rather thanutilizing the rotary switch 44 shown in FIG. 1. Also the valving couldbe so arranged to reduce the number of valves,

for example, by utilizing valves 86, 85 and 83 to release y toatmosphere rather than valve 87. Provision may also be made to reclaimand retain the oil in the air conditioning system prior to and duringevacuation of the refrigerant.

I claim as my invention.

1. Apparatus for diagnosis and servicing of an automobile airconditioning system using a refrigerant, comprising a housing;

a plurality of pressure and temperature indicating devices adapted to beconnected to said automobile air conditioning system and capable ofproviding an indication of a defective condition of said automobile airconditioning system;

an evacuating system contained within said housing capable ofwithdrawing all of said refrigerant from said air conditioning system;

charging means contained within said housing capable of holding asufficient amount of refrigerant to fully recharge said automobile airconditioning system;

a plurality of flow paths interconnecting said automobile airconditioning system, said evacuating system, said refrigerant chargingmeans, and atmosphere;

a plurality of motor operated valves selectively operable tointerconnect said flow paths;

motor means for said motor operated valves; and

means for actuating different combinations of said valves to selectivelyestablish different combinations of said flow paths.

2. The apparatus of claim 1 wherein said means for actuating differentcombinations of said valves includes a plurality of manually operatedactuators, one for each of a plurality of test or repair operations,electrically connected to said motor means for said motor operatedvalves and wherein actuation of said manually operated actuatorsoperates as many as three of said motor operated valves.

3. The apparatus of claim 1. further comprising capacitive measurementmeans integrally formed with said charging cylinder wherein the mass ofrefrigerant in both liquid and vapor form may be accurately detectedprior to charging into said air conditioning system.

4-. The apparatus of claim 1 further comprising heating means thermallyconnected to said charging means and temperature sensing means thermallyconnected to said charging means and electrically connected to saidheating means whereby said temperature sensing means intermittentlyactuates said heating means to maintain a suitably high temperature insaid charging means to maintain temperature stability and assurecomplete discharge of said refrigerant.

5..The apparatus of claim 1 wherein said plurality of pressure andtemperature indicating devices includes at least one with indiciainscribed thereon which is utilized to indicate a pressure in said airconditioning system and further having at least two additional sets ofindicia so inscribed on the meter face so that a range of ambienttemperature is referenced in such a manner that if the indication ofsaid meter falls within said range, said air conditioning system isoperating satisfactorily.

6. The apparatus of claim 5 wherein said two additional sets of indiciainscribed on said meter face are inscribed in units of temperature andare circumferentially displaced so that one set is in radial alignmentwith the lowest permissible pressure for any given temperature and theother set is in radial alignment with the highest permissible pressurefor said given temperature whereby an operator can determine for anygiven temperature whether the pressure is within the permissible rangefor that temperature.

7. A meter face for indicating a range of permissible pressure for agiven temperature, comprising a pressure scale with indicia inscribedthereon in units of pressure;

a first temperature scale with indicia inscribed thereon in units oftemperature and aligned with said pressure scale so that for any giventemperature the lowest permissible pressure is indicated concurrentlywith said given temperature; and

second temperature scale with indicia inscribed thereon in units oftemperature offset from said first temperature scale and aligned withsaid pressure scale so that for any given temperature the highestpermissible pressure is indicated concurrently with said giventemperature, whereby an observer can determine whether the desired rangeof pressure is achieved by determining whether a given pressure fallswithin the temperature range limited by said first temperature scale andsaid se'ond tem eratu e cale. 8. The appar tus o c aim 1 wherein saidcharging means includes a container suitable for containing saidrefrigerant and which further comprises a first conductive surfaceintegrally formed with said container or offset therefrom and extendingto the bottom thereof;

a second conductive surface spaced from said first conductive surfaceand electrically insulated therefrom extending to the bottom of saidcontainer except for a passageway to allow said liquid to flow betweensaid conductive surfaces;

electrical connecting means connected to said first conducting surfaceand said second conductive surface; and

electrical measuring means connected to said electrical connecting meanssuitable to determine the capacitance existing between said first andsecond conducting surface whereby the mass of both liquid and vapor ofsaid refrigerant can be determined.

9. The apparatus of claim 8 wherein said container comprises an outerhousing forming the. side wall of said container; a top formed so thatit hermetically seals said housing to form said container; and at leastone tie rod extending the length of said container to hold the top onsaid outer housing and wherein said outer housing and said tie rod areformed of the same material whereby they are equally expansible so thatthe apparatus maintains a suitable seal during temperature changes. 7

10. The apparatus of claim 8 further comprising heating means thermallyconnected to said charging means and temperature sensing means thermallyconnected to said charging means and electrically connected to saidheating means whereby said temperature sensing means intermittentlyactuates said heating means to maintain a suitably high temperature insaid charging means to maintain temperature stability and assurecomplete discharge of said refrigerant.

11. The apparatus of claim 1 further comprising means for indicatingengine speed electrically connected to said automobile whereby anoptimum operating speed can be maintained during testing.

1. Apparatus for diagnosis and servicing of an automobile air conditioning system using a refrigerant, comprising a housing; a plurality of pressure and temperature indicating devices adapted to be connected to said automobile air conditioning system and capable of providing an indication of a defective condition of said automobile air conditioning system; an evacuating system contained within said housing capable of withdrawing all of said refrigerant from said air conditioning system; charging means contained within said housing capable of holding a sufficient amount of refrigerant to fully recharge said automobile air conditioning system; a plurality of flow paths interconnecting said automobile air conditioning system, said evacuating system, said refrigerant charging means, and atmosphere; a plurality of motor operated valves selectively operable to interconnect said flow paths; motor means for said motor operated valves; and means for actuating different combinations of said valves to selectively establish different combinations of said flow paths.
 2. The apparatus of claim 1 wherein said means for actuating different combinations of said valves includes a plurality of manually operated actuators, one for each of a plurality of test or repair operations, electrically connected to said motor means for said motor operated valves and wherein actuation of said manually operated actuators operates as many as three of said motor operated valves.
 3. The apparatus of claim 1 further comprising capacitive measurement means integrally formed with said charging cylinder wherein the mass of refrigerant in both liquid and vapor form may be accurately detected prior to charging into said air conditioning system.
 4. The apparatus of claim 1 further comprising heating means thermally connected to said charging means and temperature sensing means thermally connected to said charging means and electrically connected to said heating means whereby said temPerature sensing means intermittently actuates said heating means to maintain a suitably high temperature in said charging means to maintain temperature stability and assure complete discharge of said refrigerant.
 5. The apparatus of claim 1 wherein said plurality of pressure and temperature indicating devices includes at least one with indicia inscribed thereon which is utilized to indicate a pressure in said air conditioning system and further having at least two additional sets of indicia so inscribed on the meter face so that a range of ambient temperature is referenced in such a manner that if the indication of said meter falls within said range, said air conditioning system is operating satisfactorily.
 6. The apparatus of claim 5 wherein said two additional sets of indicia inscribed on said meter face are inscribed in units of temperature and are circumferentially displaced so that one set is in radial alignment with the lowest permissible pressure for any given temperature and the other set is in radial alignment with the highest permissible pressure for said given temperature whereby an operator can determine for any given temperature whether the pressure is within the permissible range for that temperature.
 7. A meter face for indicating a range of permissible pressure for a given temperature, comprising a pressure scale with indicia inscribed thereon in units of pressure; a first temperature scale with indicia inscribed thereon in units of temperature and aligned with said pressure scale so that for any given temperature the lowest permissible pressure is indicated concurrently with said given temperature; and a second temperature scale with indicia inscribed thereon in units of temperature offset from said first temperature scale and aligned with said pressure scale so that for any given temperature the highest permissible pressure is indicated concurrently with said given temperature, whereby an observer can determine whether the desired range of pressure is achieved by determining whether a given pressure falls within the temperature range limited by said first temperature scale and said second temperature scale.
 8. The apparatus of claim 1 wherein said charging means includes a container suitable for containing said refrigerant and which further comprises a first conductive surface integrally formed with said container or offset therefrom and extending to the bottom thereof; a second conductive surface spaced from said first conductive surface and electrically insulated therefrom extending to the bottom of said container except for a passageway to allow said liquid to flow between said conductive surfaces; electrical connecting means connected to said first conducting surface and said second conductive surface; and electrical measuring means connected to said electrical connecting means suitable to determine the capacitance existing between said first and second conducting surface whereby the mass of both liquid and vapor of said refrigerant can be determined.
 9. The apparatus of claim 8 wherein said container comprises an outer housing forming the side wall of said container; a top formed so that it hermetically seals said housing to form said container; and at least one tie rod extending the length of said container to hold the top on said outer housing and wherein said outer housing and said tie rod are formed of the same material whereby they are equally expansible so that the apparatus maintains a suitable seal during temperature changes.
 10. The apparatus of claim 8 further comprising heating means thermally connected to said charging means and temperature sensing means thermally connected to said charging means and electrically connected to said heating means whereby said temperature sensing means intermittently actuates said heating means to maintain a suitably high temperature in said charging means to maintain temperature stability and assure complete discharge of said refrigerant.
 11. The apparatus of Claim 1 further comprising means for indicating engine speed electrically connected to said automobile whereby an optimum operating speed can be maintained during testing. 